#include <iostream>
using namespace std;

const int N = 50;
int dp[N];
int n;

int main()
{
    cin >> n;

    dp[0] = 1, dp[1] = 1;
    for (int i = 2; i <= n; i++)
        dp[i] += dp[i - 1] + dp[i - 2];

    cout << dp[n];

    return 0;
}
